Hrs-2 is an ATPase that has been implicated in a variety of cellular processes by virtue of its functional protein interactions. We have determined that the form of hrs-2 with the highest specific ATPase activity is an oligomer of six subunits. However, the structure of this complex is unknown. Consequently, the extensive functional studies lack a structural basis for their interpretation. Our goal is to use three-dimensional electron microscopy to determine the structure of hrs-2 and its functional complexes. We show in the preliminary results that hrs-2 can be isolated in sufficient quantities to visualize it in the electron microscope and that the data collected is of sufficient quality to perform a three-dimensional reconstruction of this protein. Association of hrs-2 with interacting proteins as well as its intrinsic ATPase activity likely plays a role in its function. Within the framework of this proposal, we will investigate the role of the ATPase activity and interacting proteins in the structure of the hrs-2 oligomer. To achieve this goal, we will employ three-dimensional electron microscopy and further refine the results using computational structure prediction methods. This structural information will provide insight into the role of interacting proteins and enzyme activity on the conformation of the hrs-2 oligomer and ultimately on its function. The Specific Aims are: (1) Three-dimensional electron microscopy of the native structure of hrs-2. (2) High-resolution structure of the hrs-2 by cryo-electron microscopy and structure prediction methods. (3) Determination of the role of hrs-2-interacting proteins on the structure of hrs-2. (4) Determination of the effect of ATP binding on the structure of hrs-2. (5) Determination of the structural basis for the mechanism by which hrs-2 inhibits SNARE complex formation.